Intelligent Network services are well known in the state of the art telecommunications networks such as GSM (Global System for Mobile communications).
The central component of the Core Network subsystem of a GSM network is the Mobile services Switching Center (MSC). It acts like a switching node of the PSTN or ISDN, and additionally provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. These services are provided in conjunction with several functional entities, which together form the Core Network subsystem. A Gateway MSC (GMSC) provides the connection to the fixed networks (such as the PSTN or ISDN). Signaling between functional entities in the Core Network subsystem uses Signaling System Number 7 (SS7), used for trunk signaling in ISDN and widely used in current public networks.
The Home Location Register (HLR) and Visitor Location Register (VLR), together with the MSC, provide the call-routing and roaming capabilities of GSM. The HLR contains all the administrative information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile station. The location of the mobile station is typically in the form of the signaling address of the VLR associated with the mobile station. There is logically one HLR per GSM network, although it may be implemented as a distributed database.
The VLR contains selected administrative information from the HLR, necessary for call control and provision of the subscribed services, for each mobile station currently located in the geographical area controlled by the VLR and currently served by that VLR. Although each functional entity can be implemented as an independent unit, currently all manufacturers of switching equipment implement the VLR together with the MSC, so that the geographical area controlled by the MSC corresponds to that controlled by the VLR, thus simplifying the signaling required. The MSC contains no information about particular mobile stations; this information is stored in the location registers.
Next, a typical incoming call setup (mobile terminating call) in a GSM network is described.
When a subscriber places a call to a mobile phone, he dials the telephone number associated with the phone user, the so-called Mobile Station ISDN (MSISDN) number, and the call is routed to the mobile phone operator's Gateway MSC. A gateway is a node used to interconnect two networks. The gateway is often implemented in an MSC, in which case the MSC is referred to as the GMSC. The GMSC acts as the “entrance” from exterior portions of the Public Switched Telephone Network onto the provider's network.
As noted above, the phone is free to roam anywhere in the operator's network or on the networks of roaming partners, including in other countries. So the first job of the Gateway MSC is to determine the current location of the mobile phone in order to connect the call. It does this by consulting the HLR, which, as described above, knows which Visited Location Register (VLR) the phone is associated with at the moment, if any.
When the HLR receives this query message, it determines whether the call should be routed to another number (called a divert), or the call should be routed directly to the mobile station of the called subscriber.
If the owner of the phone has previously requested that all incoming calls be diverted to another number, which supplementary service is also known as Call Forwarding Unconditional (CFU) to a Forwarded-to-Number (FTN), then this FTN is stored in the HLR. If that is the case, then the FTN is returned to the Gateway MSC for immediate routing to that destination.
If the mobile station is not currently associated with a VLR (e.g. because the phone has been turned off), then the HLR returns a number known as the Call Forwarding Not Reachable (CFNRc) number to the GMSC, and the call is forwarded there. Many operators may set this value automatically to the phone's voice mail number, so that callers may leave a message.
Finally, if the HLR knows that the phone is in the jurisdiction of a particular VLR, then it will request a temporary number, a so called Mobile Station Roaming Number (MSRN) from that VLR. This number is relayed to the GMSC, which uses it to route the call to another MSC, called the Visited MSC (VMSC).
When the call is received by the VMSC, the MSRN is used to find the phone's record in the VLR. This record identifies the phone's location area. Paging occurs to all mobile phone masts in that area. When the subscriber's mobile responds, the exact location of the mobile is returned to the VMSC. The VMSC then forwards the call to the appropriate phone mast, and the phone rings. If the subscriber answers, a speech path is created through the VMSC and GMSC back to the network of the person making the call, and a normal telephone call follows.
It is also possible that the phone call is not answered. If the subscriber is busy on another call (and call waiting is not being used), then the VMSC routes the call to a pre-determined Call Forwarding Busy (CFB) number. Similarly, if the subscriber does not answer the call after a period of time (typically 30 seconds), then the VMSC routes the call to a pre-determined Call Forwarding No Reply (CFNRy) number. Once again, the operator may decide to set this value by default to the voice mail of the mobile so that callers can leave a message.
An Intelligent Network (IN) is a network that is coupled to a telecommunications network that enables operators to deploy operator-specific Value Added Services (VAS). The intelligence that resides in the switch is augmented by intelligence from the Intelligent Network, which is placed in computer nodes that are distributed throughout the network. This provides the network operator with the means to develop, deploy and control services more efficiently. New services can be rapidly introduced into the telecommunications network. Once introduced, services are easily customized to meet individual customers' needs.
IN services are typically provided by a Service Control Point (SCP). An SCP is a control computer that communicates with other nodes and entities in the telecommunications network. The SCP comprises the service logic of one or more IN services and optionally IN service subscription data that allows the SCP to execute an IN service in accordance with the specific settings of a subscriber, i.e. tailor the service execution to the subscriber. When a call is established, the telecommunications network may query the SCP and ask for instructions for handling this call. For instance, an SCP is consulted to provide the translation of an 800 number to an actual phone number and to bill the owner of the 800 number for the call. SCPs may be physically separated from other components of the Intelligent Network or may be combined with these other components into a single node.
In a GSM network the IN service subscription information is stored in the HLR. Two types of information reside in the HLR: (1) static subscriber information and (2) dynamic subscriber information. The latter is e.g. needed to allow incoming calls to be routed to the mobile subscriber. The HLR stores, amongst others:                the International Mobile Subscriber Identity (IMSI); an internal subscriber identity used only by the network;        MSISDN number;        VLR address;        subscriber data on supplementary services.        
IN services may be divided into two categories. One category comprises services to be invoked for subscribers who initiate a call (Mobile Originated Call—MOC). These services are called Mobile Originating (MO) services. An example of an MO service is outgoing call screening.
Each IN service subscriber is marked in his HLR with an Originating CAMEL Subscription Information (O-CSI) element, which is used to identify a specific service at the SCP. The O-CSI initiates the triggering of the MOC service as soon as the subscriber initiates a MO call. In the above example CAMEL is deployed, which stands for “Customised Applications for Mobile network Enhanced Logic”. CAMEL was developed as a standard for extending landline IN telephony services such as call waiting and call forwarding to GSM mobile phones.
The other category comprises services to be invoked for subscribers who receive a call (Mobile Terminated Call—MTC). These services are called mobile terminating (MT) services. Examples of mobile terminating services are call diversion services and Personal Greeting Service (PGS). PGS is a service that is associated with a roaming leg. PGS entails that when a signalling connection is established between a GMSC and VMSC (a so called “roaming leg”), then a personalised greeting is played to the calling party. The personalised greeting replaces the conventional alerting tone (“ring tone”). As such, the personalised greeting is primarily related to the establishment of the roaming leg; the ring tone becomes active only when the roaming leg is established and the called party is alerted. Each IN service subscriber is marked in his HLR with a Terminating CAMEL Subscription Information (T-CSI) flag, which is used to identify a specific service at the SCP. This initiates the triggering of the MTC service during a call attempt to the subscriber.
According to the state of the art, a control node may query a HLR during MTC handling to obtain instructions from the HLR. The control node may be a GMSC. In response to the query by the control node, the HLR may send IN trigger information for the terminating call. The IN trigger information exchanged between the HLR and the control node has been standardized. For example T-CSI is the GSM standardized IN trigger information for terminating calls, as specified by 3GPP (3rd Generation Partnership Project) in 3GPP TS 29.002. IN trigger information comprises among others the address of the SCP where the IN service resides and the service key, which identifies a particular IN service within the SCP.
The control node uses the IN trigger information to invoke the IN service in the SCP as specified for the subscriber in the IN trigger information. In response to the service invocation, the SCP sends an instruction to the control node to e.g. continue call set up or to terminate the call depending on the outcome of the service execution. Current networks are typically arranged to handle a single invocation of an IN service for an MTC. Recent developments show however, that there is a need to invoke two or more IN services during terminating call handling.
Patent application WO00/25528 discloses a Service Interaction Manager, which is included in an SCP. The task of the Service Interaction Manager is to determine which of the available services in the SCP should be executed for a subscriber and to invoke those services in a particular sequence.